1. Field of the Invention
This invention relates to an image forming apparatus for transferring a developer image to a transfer material from an image bearing member through a transfer medium.
2. Description of the Related Art
An image forming apparatus having a development means in which an electrostatic latent image formed on the surface of a photosensitive drum constituting an image bearing member is developed by the toner in a powder developer is widely put into practical use. FIG. 8 is a diagram for explaining the essential parts of the conventional image forming apparatus. The image forming apparatus shown in FIG. 8 is a full-color electrophotographic image forming apparatus having at least one (for example, four) photosensitive drum 1 as an image bearing member and an intermediate transfer belt 51 as a transfer medium. Around the photosensitive drum 1, a charger 2, an exposure unit 3, a development unit 4, a photosensitive member cleaner 6, and the like are arranged and make up a process unit P constituting an image forming means. The developer image formed on the photosensitive drum 1 is primarily transferred sequentially in a primary transfer unit N1 onto an intermediate transfer belt 51 of an intermediate transfer unit 5 and is further secondarily transferred to a transfer material S such as paper in a secondary transfer unit N2.
The deposited materials remained on the photosensitive drum 1 (mainly the toner remained after the primary transfer) such as the toner  after toner image transfer are removed by the photosensitive member cleaner 6. The cleaning blade 61 of the photosensitive member cleaner 6 is pressed against the photosensitive drum 1 at a predetermined angle and a predetermined pressure, and recovers the toner and the like remaining on the surface of the photosensitive drum 1. The photosensitive drum 1 from which the remaining toner has been removed by the photosensitive cleaner 6 is returned to the charging process and the aforementioned series of the image forming operation are repeated.
The deposited materials remained on the intermediate transfer belt 51 (mainly the toner remained by the secondary transfer) such as the toner is basically removed by a belt cleaner 55. The belt cleaner 55 is arranged downstream of the secondary transfer unit N2 in the rotational direction of the intermediate transfer belt 51, and may be configured of a blade or a fur brush impressed with a predetermined voltage or the like.
Further, a configuration has been conventionally proposed in which the residue on the intermediate transfer belt 51 is recovered by the photosensitive member cleaner 6 of the photosensitive drum 1. Specifically, a voltage of opposite polarity to the toner, or the like is applied to the primary transfer roller 53 in the primary transfer unit N1 so that the toner, or the like on the intermediate transfer belt 51 is transferred to the photosensitive drum 1 (by movement in the opposite direction to the primary transfer), and the photosensitive drum 1 is cleaned by the photosensitive member cleaner 6.
Meanwhile, the cleaning blade 61 of the photosensitive member cleaner 6 cleans by rubbing the surface of the photosensitive drum 1. The toner and the additives remained on the surface of the photosensitive drum 1 after the first transfer process plays an important role in holding the lubricity between the blade and the surface of the photosensitive drum. The use of an additive which improves the lubricity such as titanium oxide or alumina fine powder, or an additive which improves the grinding performance such as strontium titanate powder, cerium oxide powder or calcium titanate powder is effective. Specifically, these additives improve the lubricity of the surface of the photosensitive drum, and prevents the components of the toner from being attached on the surface of the photosensitive drum and the image quality from being deteriorated and the smoothness of the cleaning blade from being deteriorated by increasing the friction coefficient of the surface of the photosensitive drum.
In the case where an image is formed by such image forming apparatus, on the other hand, the photosensitive drum may rotate for a long time without being supplied with the developer in the case where a conveyance path of the transfer material is long or an interval between the image forming sessions is long. As long as the photosensitive drum is rotated without being supplied with the toner, the amount of the toner and the additive having the lubrication effect between the photosensitive drum and the cleaning blade is reduced. The resulting rotation of only the photosensitive drum and the cleaning blade especially made of an elastic body increases the friction force between the photosensitive drum and the blade and deteriorates the smoothness of the cleaning blade. Once this state is maintained, the problem is caused such as the image flow due to the deterioration of the drum surface, the cut, twist, wear or noise of the blade.
To solve this problem, Japanese Patent Application Laid-open (JP-A) No. 2002-072713 discloses a method in which the developer is supplied to the drum cleaning unit between and after image forming sessions as a special control operation to supply the toner to the cleaning unit.
According to the technique proposed according to the JP-A No. 2002-072713, however, the developer is required to be supplied to and recovered from the photosensitive drum at timings other than image formation. Therefore problems such as generation of a standby time in the operation of the image forming apparatus or reduction in the productivity (number of images formed per unit time) have occurred.